Open the project containing the audio track you wish to reverse. Within the track, click on the appropriate clip. The appearance of the clip will change to indicate it is selected.
Select "Process" from the toolbar. Click "Audio" from the drop-down menu, then click on "Reverse." Your selected clip is now reversed. Continue with other clips that require treatment.
Reverse MIDI tracks by first converting MIDI to audio. There is no equivalent process for MIDI data. Consult the manual or help files for your version of SONAR for MIDI-to-audio conversion.